The present invention relates to a vehicle transmission having seven forward gears and one reverse gear, the first forward gear being a crawling gear.
Modern manual shift transmissions for vehicles often exhibit six forward gears and a reverse gear. The first forward gear is usually designed to be relatively short. That is, it exhibits a large transmission ratio. The first gear has to be designed in such a manner that it is possible to accelerate with a full load from a full stop under all customary driving conditions, in particular on steep slopes. Therefore, the maximum speed that can be reached in first gear is relatively low. Consequently one has to shift relatively early into second gear. In most vehicles with manual shift transmissions, one has to shift into third gear already at a speed of less than 100 km/h. From the viewpoint of minimizing consumption, a longer first gear and in the maximum speed range at least one overdrive gear may be preferred.
A longer “normal starting gear” may be advantageous from a consumption viewpoint. However, a long first gear presents a problem when accelerating under full load from a complete stop, for example, on a hill.
The embodiments of the invention provide a transmission that enables a reliable start in all customary driving situations and that offers consumption-related advantages over conventional transmissions. In addition, the transmission exhibits a very compact construction.
According to exemplary embodiments of the invention, the vehicle's “normal driving mode” may be represented by six “normal” forward gears. The term “normal driving mode” is defined here as comprising all driving conditions, in particular all start conditions, except for starting on steep slopes and/or on slopes when the vehicle is heavily loaded. For relatively rare driving situations, where acceleration from a full stop occurs on a hill having a steep slope or on a slope when the vehicle is heavily loaded, a crawling and/or hill gear is provided, which may, for example, use a very short gear ratio.
The exemplary embodiments of the invention are used to integrate a crawling and/or hill gear into a conventional six gear shift transmission without increasing the structural dimensions of the transmission, in particular without having to have an additional gear set plane. An exemplary transmission, according to the invention, may include an input shaft as well as an output shaft, arranged coaxially to the input shaft, and an auxiliary shaft, which is arranged parallel to the input shaft and to the output shaft. In conformity with the six gear manual shift transmission that is currently being manufactured, for example by BMW AG, of Munich, Germany, the transmission includes seven gear set planes. Each of the gear set planes is formed by a gearwheel stage, which includes a first gearwheel and a second gearwheel that meshes with the first gearwheel. Each gearwheel stage includes a gearwheel, which is connected in a rotationally fixed manner to its assigned shaft, and a gearwheel, which is rotationally mounted on its assigned shaft and is rotationally coupled to the assigned shaft by using an assigned shifting element.
According to the invention, one of the exemplary gearwheel stages is “used twice.” The term “dual use” is defined to mean that in a forward gear, intended for normal driving, the torque is transmitted from the first gearwheel of the exemplary gearwheel stage to the second gearwheel of the gearwheel stage. When the crawling and/or hill gear is engaged, the torque is transmitted in the opposite direction, i.e., from the “second gearwheel” to the “first gearwheel.” Thus, according to the invention, it is possible to expand a conventional six gear shift transmission to include a crawling and/or hill gear without having to have an additional gear set plane.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.